The present invention relates to a shear pad assembly adapted to be positioned between a rail car side frame pedestal and the rail car roller bearing adapter, and more specifically, to such a shear pad assembly which includes an elastomer positioned between spaced upper and lower plates and metal shims for reinforcing and supporting the elastomer.
Shear pads have long been known in the rail car art for use in supporting the truck side frames on the wheelsets. Initially, such shear pad assemblies utilized metal wear surfaces which permitted limited lateral and longitudinal movement of the side frames relative to the roller bearing adapters positioned on the wheelsets. Subsequently, elastomeric mountings took the place of the metal wear surfaces to provide control flexibility in all directions, particularly for self-steering rail car trucks.
U.S. Pat. No. 5,237,933 improved the elastomeric mounting by the addition of a single metal shim which extended generally throughout the elastomer with the stated advantage of significantly increasing the service life of the shear pad. One aspect of the shear pad described in the ""933 patent was to increase the thickness of the elastomeric layer adjacent its edge, as compared with the thickness at the center of the elastomer to reduce the edge strains imposed on the shear pad. This stated advantage, however, did not prove to be correct in that the reduction of the elastomer thickness adjacent its center resulted in separation of the elastomer under prolonged loading. The present invention provides an elastomer which is more uniform throughout the cross section of its thickness, resulting in more uniform shear which has the effect of spreading the shear load imposed on the pad more uniformly across the pad, eliminating the concentration of shear strain present in pads of the type shown in the ""933 patent.
The present invention relates to shear pad assemblies for use in rail car trucks to support the side frames on the wheelset roller bearing adapters and more specifically, to a shear pad for the use described which has an improved reinforced elastomer.
A primary purpose of the invention is to provide a shear pad assembly as described in which the elastomer, positioned between upper and lower plates of the shear pad assembly, has a pair of spaced reinforcing shims.
Another purpose of the invention is to provide a shear pad assembly as described in which the elastomer is substantially uniform across its cross sectional area to spread the shear load relatively uniformly across the pad.
Another purpose of the invention is to provide a shear pad assembly which does not concentrate the shear load at the center area of the pad.
Another purpose of the invention is to provide a shear pad assembly having shims to stiffen the elastomer edges so that the overall stiffness of the pad is generally uniform.
Another purpose of the invention is to provide a shear pad assembly as described in which the maximum shear strain is reduced, but the overall shear strain is more uniform throughout the thickness of the cross sectional area of the elastomer.